Downhole temperature calculation

1. A method of calculating a value representative of a downhole temperature in a hydrocarbon well, wherein the hydrocarbon well comprises a production tubing inside an outer tubing, an annulus is provided between the production tubing and the outer tubing, and the annulus receives a hydraulic control line supplying hydraulic fluid for the control of a downhole device, the method comprising:

sensing a pressure of the hydraulic fluid in the hydraulic control line at a wellhead; and

using the sensed pressure of the hydraulic fluid in the hydraulic control line to calculate the value representative of the downhole temperature.

2. The method according to claim 1 , wherein the downhole device is at a first downhole zone, the hydrocarbon well further comprises an additional downhole device at a second downhole zone, and the annulus further receives an additional hydraulic control line supplying hydraulic fluid for the control of the additional downhole device, the method further comprising:

sensing a pressure of the hydraulic fluid in the additional hydraulic control line at the wellhead to calculate the value representative of the downhole temperature.

3. The method according to claim 2 , wherein the sensing of the pressure of the hydraulic fluid in the additional hydraulic control line is carried out at a tree at the wellhead.

4. The method according to claim 1 , wherein the sensing of the pressure of the hydraulic fluid in the hydraulic control line is carried out at a tree at the wellhead.

5. The method according to claim 1 , further comprising:

sensing a temperature of a production fluid at the wellhead; and

using the sensed temperature of the production fluid to calculate the value representative of the downhole temperature.

6. The method according to claim 5 , wherein the sensing of the temperature of the production fluid is carried out at a tree at the wellhead.